High temperature superconducting slow-wave coplanar transmission lines with normal-metal crossbars

A novel superconducting slow-wave transmission line has been prepared by overlaying a superconducting coplanar waveguide with normal metal crossbars. The crossbars increase the energy storage along the transmission line, reducing the line´s group velocity allowing for shorter delay lines. Additionally, the cross-sectional dimensions of the line are smaller than typical transmission line structures, allowing for a further reduction of delay line size. Measurements show a group velocity of about 0.12 the speed of light with low dispersion, a 25 Ω characteristic impedance, and moderate transmission loss. Because the group velocity is largely independent of any properties of the superconductor, these transmission lines exhibit excellent temperature stability and delay reproducibility